Distinct effects of Ca2+ and voltage on the activation and deactivation of cloned Ca(2+)‐activated K+ channels.

Abstract

1. Cloned large-conductance Ca2+-activated K+ channels from Drosophila (dslo) and human (hslo) were expressed in Xenopus oocytes. The effects of Ca2+ and voltage on these channels were compared by analysing both macroscopic currents and single-channel transitions.2. The activation kinetics of dslo Ca2+-activated K+ channels are strongly influenced by the intracellular Ca2+ concentration, but are only minimally affected by membrane voltage. Current activation kinetics increase more than 60-fold in response to Ca2+ concentration increases in the range 0f56-405 /M, but increase less than 2-fold by voltage changes from -60 to +80 mV. 3. The activation kinetics of hslo channels are similarly influenced by increases in Ca2+ concentration; however, these kinetics are also increased 5-to 10-fold by voltage changes from -60 to +80 mV.4. The deactivation kinetics of both dslo and hslo channels are also more Ca2+ sensitive than voltage sensitive. Increasing concentrations of Ca2+ slow deactivation kinetics more than 40-fold, while changes in the membrane voltage cause less than 2-fold changes.

Ethanol sensitivity of BKCa channels from arterial smooth muscle does not require the presence of the β1-subunit

“…3). This value is similar to values reported for other slo channels expressed in Xenopus oocytes (11,16,18,28), after reconstitution into artificial lipid bilayers (13), and for arterial smooth muscle BK Ca channels studied either in situ (19,43) or in lipid bilayers (52). From the slope factor, the effective valence (z; see Ref.…”

“…Thus the bslo channel exhibits at least two open and two closed states, which is consistent with a previous model proposed for other slo channels (16). In the presence of 50 mM EtOH, time constants were 1.9 (22%) and 65.1 (78%) ms.…”

“…EtOH targets specific channel dwell states, leading to a reversible reduction in P o (see above). In BK Ca channels, whether native or cloned slo subunits, the gating process(es) that determine steady-state P o are controlled by transmembrane voltage (14,16,38). Thus we explored whether EtOH inhibition of bslo channel activity occurs by (or with) a drug-induced modification of the voltage dependence of channel gating.…”

“…A parallel shift in the voltage activation curve of BK Ca channels, whether native (6,44) or cloned from slo genes (14,16), toward positive potentials is observed when the Ca i 2ϩ that is effectively recognized by the "Ca 2ϩ sensor(s)" of the channel is effectively reduced. Thus it is possible that EtOH reduces bslo channel activity by decreasing the channel apparent Ca 2ϩ sensitivity.…”

The activation mechanism of rat vanilloid receptor 1 by capsaicin involves the pore domain and differs from the activation by either acid or heat

“…Female Xenopus laevis were obtained from Nasco (Fort Atkinson, WI). Oocytes were surgically removed and defolliculated as described previously (10). Cells were voltage-clamped near the chloride equilibrium potential (Ϫ25 mV) to minimize the contribution of endogenous Ca 2ϩ -activated Cl Ϫ channels.…”